The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation. Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A241845 a(1)=1; for n >1 a(n) is the smallest prime divisor of the number obtained from concatenation of 1 and the first n-1 composites. 5
 1, 2, 2, 2, 37, 2, 2, 2, 5, 2, 2, 2, 27793, 2, 2, 3, 2, 29, 2, 2, 2, 19, 2, 5, 2, 2, 1468910121415161820212224252627283032333435363839, 2, 2, 2, 5, 2, 2, 3, 2, 127, 2, 2, 5, 2, 3, 2, 2, 2, 3, 2, 3, 2, 2 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(1)=1, and for n > 1 a(n) is the smallest prime divisor of the number obtained from the concatenation of A018252(j), j=1, ..., n. - Wolfdieter Lang, May 07 2014 LINKS Jinyuan Wang, Table of n, a(n) for n = 1..185 EXAMPLE 1 U 4 = 14 and its divisors are 1, 2, 7, 14. Then a(2) = 2. 14 U 6 = 146 and its divisors are 1, 2, 73, 146. Then a(3) = 2. 146 U 8 = 1468 and its divisors are 1, 2, 4, 734, 367, 1468. Then a(4) = 2. 1468 U 9 = 14689 and its divisors are 1, 37, 397, 14689. Then a(5) = 37. Etc. MAPLE with(numtheory): T:=proc(t) local x, y; x:=t; y:=0; while x>0 do x:=trunc(x/10); y:=y+1; od; end: P:=proc(q) local a, b, n; b:=1; print(1); for n from 2 to q do if not isprime(n) then b:=n+b*10^T(n); a:=sort([op(divisors(b))]); print(a); fi; od; end: P(10^6); # Paolo P. Lava, Apr 30 2014 CROSSREFS Cf. A018252, A075019, A104644, A132934. Sequence in context: A147975 A083148 A318166 * A254131 A175910 A257662 Adjacent sequences:  A241842 A241843 A241844 * A241846 A241847 A241848 KEYWORD nonn,base AUTHOR Paolo P. Lava, Apr 30 2014 EXTENSIONS More terms from Jinyuan Wang, Jun 27 2020 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 13 02:09 EDT 2020. Contains 336441 sequences. (Running on oeis4.)